Solar control coating systems are known. For example, commonly owned U.S. Pat. No. 5,688,585 discloses a solar control coated article including: glass/Si3N4/NiCr/Si3N4. One object of the '585 patent is to provide a sputter coated layer system that after heat treatment is matchable colorwise with its non-heat treated counterpart. While the coating systems of the '585 patent are excellent for their intended purposes, they suffer from certain disadvantages. In particular, they tend to have rather high emissivity values (e.g., because no silver (Ag) layer is disclosed in the '585 patent).
Low-emissivity (low-E) coating systems are also known in the art. For example, commonly owned U.S. Pat. No. 5,376,455 discloses: glass/Si3N4/NiCr/Ag/NiCr/Si3N4. Low-E coating systems such as this are typically designed for maximum visible transmission. For this reason, the NiCr layers are made rather thin. This enables high transmission and low-E characteristics, but less than desirable solar control (e.g., shading coefficient) characteristics. Thus, the low-E coating system of the '455 patent is unfortunately not sufficiently color matchable after heat treatment with its non-heat treated counterpart, and lacks superior solar control characteristics such as shading coefficient (SC).
Accordingly, when it is desired to provide an insulating glass (IG) unit with both low emissivity (low-E) and solar control characteristics, it has often been necessary to combine the solar control coating of the '585 patent with the low-E coating of the '455 patent in a single IG unit. For example, the solar control coating of the '585 patent is placed on the #2 surface of the IG unit while the low-E coating of the '455 patent is placed on the #3 surface of the IG unit. The need for these two separate and distinct coatings in an IG unit is undesirable, for cost, processing and/or performance reasons.
The need for matchability (before heat treatment vs. after heat treatment) is also known. Glass substrates are often produced in large quantities and cut to size in order to fulfill the needs of a particular situation such as a new multi-window and door office building, vehicle windshield needs, etc. It is often desirable in such applications that some of the windows and/or doors be heat treated (i.e., tempered, heat strengthened or bent) while others need not be. Office buildings often employ IG units and/or laminates for safety and/or thermal control. It is desirable that the units and/or laminates which are heat treated substantially match their non-heat treated counterparts (e.g., with retard to color, reflectance, and/or the like, at least on the glass side) for architectural and/or aesthetic purposes. In addition, it is sometimes desirable that certain windows, doors, windshields, etc. be of a substantially neutral color, preferably tending to the blue-green side of the spectrum.
It has in the past been possible to achieve matchability in systems other than those of the aforesaid '585 patent, but only between two different layer systems, one of which is heat treated and the other is not. The necessity of developing and using two different layer systems to achieve matchability creates additional manufacturing expense and inventory needs which are undesirable.
U.S. Pat. Nos. 6,014,872 and 5,800,933 (see Example B) disclose a heat treatable low-E layer system including: glass TiO2/Si3N4/NiCr/Ag/NiCr/Si3N4. Unfortunately, when heat treated this low-E layer system is not approximately matchable colorwise with its non-heat treated counterpart (as viewed from the glass side). This is because this low-E layer system has a ΔE* (glass side) value of greater than 4.1 (i.e., for Example B, Δa*G is 1.49, Δb*G is 3.81, and ΔL* (glass side) is not measured; using Equation (1) below then ΔE* on the glass side must necessarily be greater than 4.1 and is probably much higher than that).
In view of the above, it will be apparent to those skilled in the art that there exists a need for a coating or layer system that could satisfy both solar control and low-E requirements (e.g., so a solar control coating and a separate low-E coating need not be used together on different surfaces of the same IG unit). In addition to and/or instead of the above need, there also exists a need in the art for a low-E coating or layer system which after heat treatment substantially matches in color and/or reflection (as viewed by a naked human eye from the glass side) its non-heat treated counterpart. In other words, there exists a need in the art for a low-E matchable coating or layering system.
It is a purpose of this invention to fulfill any and/or all of the above-listed needs, and/or other needs which will become more apparent to the skilled artisan once given the following disclosure.